Dilute aqueous dispersions and their application



United States Patent M 2,714,075 DILUTE AQUEOUS DISPER IO S AND THEIR APPLICATION Frederick K. Watson and John L. Ludlow, Wilmington, and John R. Kateley, Newport, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., 2 corporationof Delaware NoDrawing. Application November 27, 1951, Serial No. 258,522 14Claims. (Cl. 1 17--6 5) This invention relates to dispersions of certain modified polyamides and to the application of these dispersions to substrates such astextile fabrics or the like.

The modified polyamides with which the present invention is concerned are the N-alkoxymethyl polyamides of the type described in theCairns Patent U. S. 2,430,860. In particular, these polyamides include the N-alkoxymethyl-modified polyhexamethylene adipamides in which from 20% to 60% of the hydrogen atoms in the original amide linkages are replaced by alkoxymethyl groups, and in which the alkoxy group contains from one to four carbon atoms.

It has been known for some time that N-alkoxymethyl polyamides of this type can be converted into dispersions. No satisfactory method has been available, however, for preparing extremely dilute dispersions of these polyamides which are .stable over long periods of time and yet which can be exhausted onto textile fabrics or the like.

It is an object of this invention to provide novel dispersions of modified polyamides. Another object of the invention is to provide dilute dispersions of modified polyamides containing agents which act as a stabilizer for the dispersion during storage and which also act as a stabilizer during the exhaustion of the dispersion 'onto a textile fabric or the like. A further object of the invention is to provide a method forapplying these dilute dispersions of modified polyamides to suitable substrates, followed, if desired, by curing of the modified polyamide. Other objects of the invention will appear hereinafter.

In accordance with this invention, it has been discovered that N-alkoxymethylpolyhexamethylene adipamides can be formed into stable, dilute aqueous dispersions by the addition of certain salts, to be defined hereinafter, which, upon application of the dispersion, serve as agents which promote the preferential exhaustion of the modified polyamide onto a textile fabric or similar article. It has also been discovered that dilute dispersions of these modified polyamides can be applied to suitable substrates, together with the salt, and the entire mixture then acidified to bring about exhaustion of the dispersion onto the substrate.

In accordance with a preferred embodiment of the invention, there are provided dilute aqueous dispersions containing from 0.01 to 0.5%, based upon the weight of the dispersion, of an N-alkoxymethylpolyhexamethylene adipamide, a dispersing agent and ammonium citrate or morpholine citrate as the stabilizing agent. N-methoxymethylpolyhexamethylene adipamides having methoxymethyl groups attached to-from 25% to 50% of the amide nitrogen atoms are preferred. I

The salts which serve as stabilizers for the dispersions of this invention are the water soluble salts of acids having an ionization constant for the first hydrogen of at least 1 10- The dispersions can be made up in any one of several different ways. Preferably, an aqueous alcoholic solution of the modified polyamide, containing adispersing agent and the stabilizing agent, is diluted witha large volume of water using moderate agitation. The dilution with water serves to insolubilize the modified polyamide in the form of very finelydivided particles which are stabilized against ,tains at least of water.

2,714,075 Patented July 26, 1955 flocculation by the dispersingagent and by the stabilizing agent. Alternately, a dilute dispersion containing the modified polyamide and the dispersing agent may first be formed and the stabilizing agent added thereto. Instill another alternative, a relatively concentrated aqueous dis.- persion of the modified polyamide may be prepared and then diluted by the addition of more water, the stabilizing agent being added either prior or subsequent to the dilution.

In preparing the dispersions, solutions of the modified polyamides in various kinds of solvents may be employed. Suitable solvents include methanol, ethanol, :phenbls,iso- .propanol, n-butanol, tertiary butanol, ;or mixtures .of one or more of these solvents with water. Mixtures of methanol or ethanol with from 10% to 50% of water are .preferred. The addition of from 1 to 10% of a higher alcohol such as benzyl alcohol, furfuryl alcohol, or combinations thereof greatly increases the stability of these alcoholic solutions.

The water and the solution of the modified polyamide may be mixed in any suitable manner, but it is preferred .to stir an alcoholic solution into the water. The rate of addition of the alcoholic solution containing the modified polyamide to the water is not critical. It 'canbe added slowly or in a single portion. Some agitation is needed, but the rate of agitation is not critical so long as a;homogeneous mixing is obtained. The dilute dispersions can be made at any temperature from room temperature up to about 200 F. It is also possible to make a dispersion at room temperature and heat it up to, say, F. or 200 F. without affecting the dispersion. The preparation may be carried out in either a batchwise or a continuous manner.

The dispersions of the present invention are aqueous dispersions, in the sense that the liquid .phase must contain at least 50% by weight of water. Preferably, the liquid phase consists primarily of water, or else con- In addition to water various other water-miscible or water-immiscible liquids may be present. It frequently happens that the dispersions are prepared from alcoholic solutions and as a result they may contain small amounts of one or more of the C1 to C4 alcohols. Other liquids such as acetone, which counteract the tendency of the alcohols to dissolve the polyamides, may also be present. 'It is preferred that purified or distilled water be employed in preparing the dispersions.

The concentration, or solids, content, of the N-alkoxymethylpolyhexamethylene adipamides in the dispersions of this invention may vary from about 0.01% to about 0.5%, based upon the total weight of the dispersion. Preferably, the concentration is within the range of from 0.05% to 0.2% .by weight. The diameter of the 'N- alkoxymethylpolyhexamethylene adipamide particles in the dispersions should be less than ten microns, and the particle diameter may go down to 0.1 micron, or even less. Preferably, the particles vary from less than 0.1 micron up to about 3 microns, and the average particle diameter is within the range of from 0.1 to 2 microns. Dispersions of this type are colloidal in nature with a consistency not much greater than water. They are ,stable for periods up to several weeks or more.

A wide variety of dispersing agents, including the anionic, cationic, and non-ionic types, may-be employed in order to prevent coagulation of the particles. Among the more useful dispersing agents are the sodium or triethanolamine salts of sulfated long-chain alcohols or sulfated branched chain secondary alcohols, the sodium salts of alkyl or aryl sulphonic acids, the alkyl aryl polyether alcohols, the quaternary ammoniumsaltssuch as stearyl ,dirnethyl benzyl ammonium chloride, casein and the like. The choice of the most .effectiveidispersing agent depends to a considerable extent upon the pH of the dispersion. For the relatively more acidic dispersions, the cationic agents, such as the quaternary ammonium compounds are preferred, while for the neutral dispersions, the anionic or non-ionic agents, and in particular the sodium alkyl sulfates, such as sodium lauryl sulfate, are preferred. Combinations of two 1' more dispersing agents, of the same type or of different types, may be employed advantageously. The dispersing agents are generally employed in amounts varying from 0.5% to and preferably from 1% to 10%, based upon the weight of the modified polyamide.

As pointed out above, the stabilizing agents which are added to the dispersions are water-soluble salts of acids having an ionization constant for the first hydrogen of at least 1x10 Suitable salts, for instance, include those derived fromv the alkali metals such as sodium and potassium, and those derived from nitrogen containing bases such as ammonia, the lower alkyl amines, the alkanol amines, the heterocyclic bases such as pyridine and morpholine, and the like. The ammonium and morpholine salts are preferred. The stabilizing agents are employed in amounts varying from 0.5% to. 10%, based upon the weight of the modified polyamide.

The acid portion of these stabilizing agents may be derived from various acids such as lactic acid, citric acid, chloracetic acid, itaconic acid, malonic acid, mesaconic acid, diglycolic acid, tartaric acid, maleic acid, hydroxyacetic acid, oxalic acid, glutaric acid, adipic acid, malic'. acid, fumaric acid, phthalic acid, salicyclic acid, propionic acid, acetic acid, formic acid, phosphoric acid,'sulfuric acid, hydrochloric acid and the like.

The citrate salts are outstanding in that they stabilize the dispersions during very long periods of storage, and they also stabilize the dispersions at a very much lower pH than do the salts of other acids. For example, ammonium citrate and morpholine citrate stabilize the dispersions at a pH as low as 2.0. At the same time, they promote exhaustion of the dispersions onto textile fabrics 1 and thus bring about complete utilization of the dispersed polymer. Because of the combination of prop- *erties, ammonium and morpholine citrate are the preferred stabilizing agents of the present invention.

Generally, the pH of the dilute dispersions, prior to the addition of acid in the step of exhausting the modified polyamide onto the substrate, is maintained within the range of from 6.5 to 7.5 during storage, and preferably within the range of from 6.8 to 7.2. It is also possible to prepare these dilute dispersions in an initially more acidic form, having a pH, for instance, of from 2.0 to 6.5, and preferably from 3.5 to 5.5, in which case cationic dispersing agents are generally used. However, substantially neutral dispersions, prepared-using non-ionic or anionic dispersing agents, are preferred in the practice of this invention, since they offer advantages in controlling the exhaustion step.

The exhaustion of the initially neutral dispersions onto textile fabrics is brought about by lowering the pH, and the speed of exhaustion can be controlled very accurately by controlling the temperature and the pH. The exhaustion generally takes place at a pH of 6.6 or less, and preferably at a pH of from 5.5 to 6.6, depending upon the bath temperature. At 150 F., for instance, the speed of exhaustion can be controlled by slow, dropwise addition of dilute citric acid to produce a pH of 6.5. At this pH, the dispersion is usually exhausted in ten minutes. At a pH of 6.2, it requires about 6 minutes, while at a'pH of 6.0, it requires about 1 minute. With .a bath temperature of about F., the times for' exhaustion are much greater. ample, at a pH of 6.5, it requires about 20 minutes for exhaustion; .at a pH of 6.2, it requires 12 minutes; and at a pH of 5.8, it requires about 1 minute.

With a slow rate of exhaustion (5 to 12 minutes) the dispersion will be deposited more evenly "on the a For exthe fabric, while at a fast rate of exhaustion the modified polyamide may be spread irregularly, with larger particles being deposited on the fabric. Any acid may be employed to bring about this exhaustion, but citric acid very much preferred. In general, best results are obtained when the dispersion bath is operated at 150 F. and exhausted at a pH of 6.2 to 6.6.

The fabric may be immersed in the dispersion either before or after acidification with good results. However, immersing the fabric in the dispersion after acidification is preferred, since this method is subject to better control of pH, with subsequent more even deposition of the modified polyamide on the substrate. The stabilizing agents of this invention are particularly advantageous in this preferred method, as they exert a profound eifect in preventing coagulation of the acidified dispersion. Alternately, the acidification may be carried out by initially acidifying the fabric itself, and then introducing the acidified fabric into the neutral or slightly acidified dispersion. Improved hand and other advantages are sometimes obtained by pretreating the fabric with a cationic agent such as stearyl dimethyl benzyl ammonium chloride.

The amount of modified polyamide which should be introduced onto the textile fabric or other substrate will depend upon the nature of the substrate and the ultimate use to which it is to be put. In general, loadings of from 0.2% to 15% of modified polyamide, based upon the weight of substrate, are employed. When treating nylon fabrics or stockings, for instance, loadings of from 0.5% to 6% are preferred.

The exhaustion of the dispersion bath can be accomplished by other methods. By one procedure, the dispersion is initially made up at a temperature of, say, F., and the citric acid or other exhausting agent is added immediately. The fabric to be treated isimmersed and the bath is heated to a temperature of about F. with agitation. The exhaustion of the bath takes place during the temperature rise, usually within 10 to 15 minutes. In another method, the dispersion is initially prepared with a cationic dispersing agent, and with the requisite amount of ammonium citrate or other stabilizing agent and the requisite amount of citric acid or other exhausting agent. The fabric is immersed in this acidic dispersion and an anionic dispersing agent is added. The two dispersing agents tend to mutually precipitateeach other, thus bringing about the exhaustion of the modified polyamide onto the fabric. The temperatures at which exhaustion takes place are generally considerably below the curing temperatures.

After exhaustion of the modified polyamide onto the fabrics the excess water is removed by any suitable method, as by drying the materials in air, by centrifuging, or the like. Alternately, the wet fabrics can be piaced directly in the curing oven, but the curing cycle must then be lengthened to compensate for the initial drying period.

Curing of the N-alkoxymethylpolyhexamethylene adipamide, either by heating, or by treating with acid, orby a combination thereof, is a very important factor in those applications where it is desired to make the ultimate product permanent, wash fast and resistant to organic solvents. The stronger the acid, the faster the curing at a given temperature. In general, curing temperatures above about C. should be avoided because they tend to damage the substrates. Although the stronger acids such as hydrochloric acidor sulphuric acid are efiective curing agents, they may cause degradation of the fabric or the finish, or, if not extracted, they may cause overcuring, brittleness, and/ or loss of adhesion by continuing to react after the temperature has been reduced'to room temperature and the product is supposedly ready for use. Accordingly, it is preferred 0 to employ the relatively weaker organic acids, such as' citric acid, maleic acid, lactic acid, and formic acid. Acids having an ionization constant of from l l0 to about 1 10- are preferred.

' When'using such acids, it is possible to'control very accur ately thedegree of "curing by controlling the temperature and the time of the curing cycle. Curing need not be carried out in those applications where wash fastness or insolubility is not necessary or desirable.

Citric acid is the preferred curing agent, because with this agent curing of the modified polyamide on the treated objects is readily brought about and controlled at temperatures of C. to 150 C. without subsequent continued curing at lower temperatures. The same citric acid which is used to bring about exhaustion of the dispersions may also be used to bring about the subsequent curing, or, if needed, additional citric acid may be added. When using citric acid as the curing agent, the curing temperature may range from about 100 C. to 150 C., and the curing cycle may range from about 1 minute to about 30 minutes, depending upon the temperature. After the desired degree of curing has been obtained, it may be advantageous, in the case of acids other than citric acid, to extract any remaining acid from the treated fabric in order to prevent any subsequent alteration in the N-alkoxymethylpolyhexamethylene adipamide with the passage of time, or any damage to the fabric. When the stabilizing agent which is employed is one which decomposes at a temperature below the curing temperature to yield an acidic residue, this acidic residue may also have a helpful effect in bringing about curing. Stabilizing agents of this type are the ammonium, lower amine, morpholine and pyridine salts. Ammonium citrate decomposes, for example, at a temperature of about C. to C. to yield ammonia, which is volatilized, and free citric acid.

Treatment of filaments, fabrics, stockings or films made of wool, cotton, rayon, nylon, acrylonitrile polymers, ethylene polymers, polyethylene terephthalate, leather, or the like, or combinations thereof, with the dilute dispersions of-the present inventionresults in improved properties such as increased abrasion resistance, increased snag resistance, anti-static properties, dye fastness, dimensional stability, increased water absorption, a better hand, a delusteringeifect, a reduction in fabric slippage and increased tensile strength. For example, a nylon tricot fabric finished with 1.1% by Weight of the cured modified polyamide has a pleasant silk-like hand and a 30-fold increase in the rate of absorption of water. Marquisette fabrics prepared from polyacrylonitrile fiber '(Orlon) or from polyethylene terephthalate fiber (Dacron) finished with 5.5% of the cured modified polyamide have a permanent stiffness and greatly enhanced fabric stability toward washing. Finishing with 0.6% of the cured modified polyamide on rayon broadcloth acts as a wrinkle resistant finish. The application of these dispersions as a binder to a fabric comprising nylon staple as the structural fiber, plus cellulose acetate as the extractable poreformer, results in an excellent leather-like product.

The following examples will illustrate certain features of the invention:

Example 1.A solution is prepared by adding 0.5 part by weight of N-methoxymethylpolyhexamethylene adipamide having the hydrogens of about 35% of the amide nitrogen atoms replaced by methoxymethyl groups to 25 parts of a solvent containing 70% of ethanol and 30% of water. To this solution there is added 0.025 part of sodium lauryl sulfate dispersing agent and 0.035 part of ammonium citrate stabilizing agent. The mixture is then heated to a temperature of about to F. under reflux to dissolve all of the modified polyamide. The resulting solution is then added in a single portion to 475 parts of water which is preheated to 150 F. To insure uniform, homogeneous distribution, the dispersion is agitated for several minutes, giving a product which is ready for the finishing applications. The resulting aqueous dispersion is opalescent in appearance with a consistency (viscosity) not much greater than that of water. The average particle diameter is less than 1 micron. The pH is within the range of 6.8 to 7.2.

Example 2.A bath containing 1500 parts by weight of the dilute dispersion prepared in accordance with Example 1 is held at about 150 F., and a dilute 1%) citric acid solution is added to adjust the pH to 6.5. Womens 15-denier monofilament hose parts by weight) are then added to the bath. The bath is agitated for 10 to 12 minutes in order to exhaust the dispersed polyamide onto the fabric. The hose are removed from the bath and placed in a centrifuge to remove excess water. The finish is then cured by heating the damp hose on boarding frames at 120 C. for 5 minutes. The resulting hose have an excellent appearance and silk-like hand, and exhibit very superior snag resistance aswell as a 30-fold increase in the rate of absorbing water. .If the stabilizing agent, in this case ammonium citrate, is omitted, the dispersion cannot be exhausted satisfactorily, since the addition of acid causes appreciable precipitation of the modified polyamide to the bottom of the bath.

Example 3.-'Womens 30-denier IO-filament hose are treated as in Example 2, except that the hose are immersed before acidification of the bath. The treated hose, as in Example 2, are improved in hand, abrasion resistance and in the rate of absorbing water.

Repeated washing with soap of nylon hose finished with modified polyamides may reduce the water absorptiveness, but subsequent washing with a non-ionic detergent restores it.

Example 4.-A number of dispersions were made up in which the ammonium citrate stabilizing agent of Example l-was either omitted or was replaced by citric acid or was replaced by another stabilizing agent. The results obtained when employing these various stabilizing agents are set forth in the following table:

Table II. lsglgbiliz- V mg m III. Deposition on I. Stabilization of Initial Neutral Dispersion igggnlailsfo Fabric (pH 55) Fabric) I 't l S11 If Lit Unit 1 1 1 i ii id D f V n1 1a e eo ia w ie isc egreeo stabmzmg Agent, pH Dispersion persion is Added Deposition Stable (cc.)**

Control (none) 7. 9 Flocculated 28 hrs 6. 2 none None. Control (with citric acid) 7. 9 .Coagulated immediately 1 Partial. Ammonium citrate 6. 8 Stable 14 days 2. 0 1 Complete. Morpholine citrate. 7. 0 do 2.0 1 Do. Ammonium sulfate 7. 5 Flocculated 16 hr 4. 0 .1 Do. Ammoniumchloride. 7. 5 do 4.0 1 Do. Ammonium adipate 7. 5 do..- 5. 5 1 Do. Ammonium acetate 7. 6 do 3.0 1 -Do. Sodium monophosphate 7. 2 do- 4.0 1 Do. Sodium triphosphate 8.9 do 3.0 3 Do.

"*1 cc. of 3% citric acid.

From this table, it can be seen that the stabilizing agents serve to prevent coagulation of the dispersion as the pH is reduced and also serve to promote effective deposition of the dispersion onto the fabrics. It can also be seen that ammonium citrate and morpholine citrate are outstanding in providing dispersions which have very long shelf life and which are resistant to coagulation at low pHs in the absence of any fabric.

The role of the citrate salts or other stabilizing agents appears to be two-fold; namely, (a) to stabilize the dispersion under acid conditions necessary to bring about exhaustion; and (b) to promote preferential exhaustion of the modified polyamide onto the fabric, instead of allowing the modified polyamide to precipitate to the bottom of the bath. The citrate salts are the preferred stabilizing agents, because, in addition, they perform the very important function of stabilizing the dispersions in the neutral state, or during storage, for very long periods of time.

The dispersions of the present invention may contain a number of different types of ingredients in addition to the modified polyamide. For example, the dispersions may contain pigments, dyes, delustering agents, other curing agents, urea, thickening agents, anti-static agents, flame-resistant or flame-retardant agents, water repellents, antioxidants, heat stabilizers such as sodium phenyl phosphinate, plasticizers such as N-ethyl toluene sulfonamide, temporary plasticizers such as diethylene glycol, agents such as stearic acid, fillers, dimensional stabilizers such as urea-formaldehyde or melamine-formaldehyde resins and the like. A given dispersion may contain two or more of the N-alkoxymethyl polyamides of the same or of different degrees of substitution. Codispersions of the modified polyamides with other natural or synthetic resins, such as natural rubber, synthetic rubber, unmodified polyamides, ethylene polymers, and the like may also be prepared.

The dispersions may be employed in the preparation of adhesives; binders; coatings for paper, furniture, bowling pins and other articles; impregnated articles; films and leather-like products. Fabrics coated with these dispersions may be used as shoe uppers. In producing films or sheets, the dispersions are cast onto a suitable surface, the water is removed by evaporation, and the film is subjected to heat to bring about agglomeration of the articles into a continuous film. 7

A big advantage of the dispersions of the present invention is that they make possible the application of modified polyamides to textile fabrics in a manner which'results in an extremely satisfactory product and which at the same time eliminates the use of inflammable and expensive solvents which were employed in prior coating processes. The dispersions are stable over long periods of time and hence can be made up well ahead of time without inconvenience. If the dispersion settles, it can be redispersed by merely reagitating. The dispersions are stable when heated to temperatures as high as 175 F. It is possible to dilute or concentrate a given dispersion either by adding more water or by flash evaporation to remove water. The application of the dispersions is readily carried out in a batchwise fashion and the rate of exhaustion onto the fabrics can easily be controlled by' controlling the amount of acid added and the temperature.

The teachings of the present invention with respect to the N-alkoxymethylpolyhexamethylene adipamides may also be applied advantageously to other soluble polyfor hydrophobic fibers, films, or fabrics of materials such as nylon, Dacron polyester fiber, Orlon acrylic fiber, and polythene. Further, these alkoxymethyl polyamides may be insolubilized in situ on the fiber or fabric,; as disclosed in U. S. Patents 2,430,860 and 2,430,933, for example, by the application of heat in therpresence of an acid catalyst, and thusrender the anti-static treatment permanent to laundering or dry cleaning. The water soluble and/or water sensitive polyamides which serve as the basis for this antistatic fiber and fabric treatment are disclosed in U. S. patents, 2,158,064, 2,191,556 and 2,274,831. The alkoxymethyl derivatives of these polymers may be prepared as described in U. S. 2,430,860. Examples of these anti-static materials are the methoxymethyl derivatives of poly-3,6-dioxaoctamethylene adipamide (which is readily soluble in water at room temperature) and the mcthoxymethyl derivatives of poly-4-oxaheptamethylene adipamide (which is soluble in 10% n-propanol).

Any of these substances may be applied to a fabric by padding or exhausting on the fabric a solution or a dispersion of the polymer and an acid catalyst. The goods so treated are then subjected to a heat treatment to insolubilize the polymer, Many of these substances possess negative temperature coefiicients of solubility which permit their application to fabrics by precipitation as an alternateprocess. In this procedure the fabric is immersed in a solution of polymer and the catalyst at room temperature. The temperatureof the solution is slowly raised causing precipitation of the polymer onto the fabric. The fabric is removed from the bath while hot and given a further heat treatment to permit insolubilization of the polymer.

Since many modifications of the processes and products described herein can be made by those skilled in the art without departing from the spirit and scope of the invention, it is to be understood that the invention is not restricted except by the claims.

We claim: V

1. An aqueous dispersion having a pH of 2.0 to 7.5 comprising from 0.01% to 0.5%, based upon the total weight of the dispersion, of an N-alkoxymethylpolyhexamethylene adipamide in the form of particles having an average diameter within the range of 0.1 to 2.0 microns and having alkoxymethyl groups attached to from 20% to 60% of the amide nitrogen atoms; a dispersing agent; and from 0.5% to 10%, based upon the weight of the N- alkoxymethylpolyhexamethylene adipamide, of a stabilizing agent comprising a water-soluble salt of a nitrogencontaining base and an acid having an ionization constant for the first hydrogen of at least l X 10 2. An aqueous dispersion in accordance with claim 1 in which the N-allroxymethylpolyhexamethylene adipamide is N-methoxymethylpolyhexamethylene adipamide.

3. An aqueous dispersion in accordance with claim 1 in which the dispersing agent is a salt of a sulfated longchain alcohol.

4. An aqueous dispersion in accordance with claim 1 in which the dispersing agent is an alkyl aryl polyether alcohol.

5. An aqueous dispersion in accordance with claim 1 in which the dispersing agent is a quaternary ammonium in which the water-soluble salt is morpholine citrate.

9. An aqueous dispersion in accordance with claim 1 in which the water-soluble salt is ammonium citrate.

10. An aqueous dispersion in accordance with claim 1 in which the water-soluble salt is ammonium citrate and in which the pH is within the range of from 6.5 to 7.5.

31. A process which comprises contacting a substrate with an aqueous dispersion having a pH of 2.0 to 7.5 comprising a dispersing agent and from 0.01% to 0.5%, based upon the total weight of the dispersion, of an N- alkoxymethylpolyhexamethylene adipamide having an average particle size of between 0.1 and 2.0 microns and having alkoxymethyl groups attached to from 20% to 60% of the amide nitrogen atoms, in the presence of a water-soluble salt of a nitrogen-containing base and an acid having an ionization constant for the first hydrogen of at least 1X10- at a pH of from 2.0 to 6.6, whereby the dispersion is substantially completely exhausted onto the substrate.

12. A process in accordance with claim 11 in which the substrate containing the N-alkoxymethylpolyhexamethylene adipamide is subjected to a heating operation in the presence of an acid material to bring about curing of the polyamide.

13. A process which comprises contacting a fabric with a bath containing an aqueous dispersion having a pH of 2.0 to 7.5 comprising a sodium higher alcohol sulfate a dispersing agent, from 0.01% to 0.5 based upon the total weight of the dispersion, of an N-methoxymethylpolyhexamethylene adipamide having an average particle size of between 0.1 and 2.0 microns and having methoxymethyl groups attached to from to of the amide nitrogen atoms, and from 0.5% to 10%, based upon the weight of the N-methoxymethylpolyhexamethylene adipamide, of ammonium citrate, the contacting of the fabric with the dispersion being effected at a temperature of from to 175 F. and at a pH of from 5.5 to 6.6 produced by the addition of citric acid to the original dispersion, whereby the dispersion is substantially completely exhausted onto the fabric; and thereafter subjecting the fabric containing the N-methoxymethylpolyhexamethylene adipamide to curing at a temperature of from C. to C. in the presence of citric acid as a curing agent.

14. A process which comprises adding a solution comprising (a) an aqueous alcohol solvent, (b) an N-alkoxymethylpolyhexarnethylene adipamide having alkoxymethyl groups attached to from 20% to 60% of the amide nitrogen atoms, (0) a sodium higher alcohol sulfate dispersing agent, and (d) ammonium citrate, to a large volume of water to produce a dilute dispersion containing from 0.01% to 0.5 of the N-alkoxymethylpolyhexamethylene adipamide having an average particle size of between 0.1 and 2.0 microns, based upon the total weight of the dispersion.

Catlin Feb. 22, 1944 Cairns Apr. 12, 1949 

11. A PROCESS WHICH COMPRISES CONTACTING A SUBSTRATE WITH AN AQUEOUS DISPERSION HAVING APH OF 2.0 TO 7.5 COMPRISING A DISPERSING AGENT AND FROM 0.01% TO 0.5%, BASED UPON THE TOTAL WEIGHT OF THE DISPERSION, OF AN NALKOXYMETHYLPOLYHEXAMETHYLENE ADIPAMIDE HAVING AN AVERAGE PARTICLE SIZE OF BETWEEN 0.1 AND 2.0 MICRONS AND HAVING ALKOXYMETHYL GROUPS ATTACHED TO FROM 20% TO 60% OF THE AMIDE NITROGEN ATOMS, IN THE PRESENCE OF A WATER-SOLUBLE SALT OF A NITROGEN-CONTAINING BASE AND AN ACID HAVING AN IONIZATION CONSTANT FOR THE FIRST HYDROGEN OF AT LEAST 1X10-5, AT A PH OF FROM 2.0 TO 6.6, WHEREBY THE DISPERSION IS SUBSTANTIALLY COMPLETELY EXHAUSED ONTO THE SUBSTRATE. 